Patent Literature 1 describes an optical fiber system in which optical transmission properties are controlled by applying a magnetic field to a filled liquid crystal to change the orientation of the liquid crystal in an optical fiber including a liquid-crystal-filled optical fiber which is formed of a hollow fiber filled with the liquid crystal.
Non Patent Literature 1 describes a capillary optical fiber including an optical core having a ring shape and a high refractive index around an air hole, an optical clad having a low refractive index, and a covering layer having a high refractive index.